COLOR STABILITY OF A NANOFILL COMPOSITE: EFFECT OF DIFFERENT IMMERSION MEDIA

Objective:

The aim of this in vitro study was to evaluate the color stability of a nanofill composite resin (Filtek Z350) in different immersion media.

Materials and methods:

Twelve resin-based composite specimens were prepared using a silicon cylindrical mold measuring ≅1mm of thickness and ≅ 10mm of diameter. Specimens were light-cured for 40 s from both sides using a LED Radii at 1400 mW/cm² and were randomized into 4 groups (n= 3) according to immersion media: coffee, yerba mate, grape juice or water (control solution). A digital spectrophotometer was used to evaluate the color changes at baseline and at 1-week after immersion in each solution. Specimens were stored in the different staining media for 4 h/day during 1 week. The color differences (ΔE) were analyzed by paired t-test and one-way ANOVA with complementary Tukey test (p<0.05).

Results:

After 1-week of immersion, a perceptive color change for the group stored in the grape juice compared to baseline (p=0.008) was observed. Coffee and yerba mate did not show any color changes visible for the human eyes or significantly different from the control group (p>0.05)

Conclusions:

The findings of the present study suggest that the tested nanofill resin-based composite was susceptible to staining by substances present in the grape juice.     

INFLUENCE OF PULSE-DELAY CURING ON SORPTION AND SOLUBILITY OF A COMPOSITE RESIN

The purpose of this study was to evaluate the sorption and solubility of a composite resin (TPH³; Dentsply) cured with halogen light due to different storage media and curing modes. The methodology was based on the ISO 4049 standard. Two independent groups were established according to the storage time (7 days-G1; 60 days-G2). A stainless steel mould (2 mm x 8 mm ø) was used. The selected curing modes were: I (Conventional - C): 40s - 600 mW/cm²; II (Pulse I - PD): 3 s - 200 mW/cm² + 2 min (delay) + 39 s - 600 mW/cm²; III (Pulse II): 10 s - 200 mW/cm² + 2 min (delay) + 37 s - 600 mW/cm²; IV (Pulse III): 3 s- 600 mW/cm² + 2 min (delay) + 37 s -600 mW/cm². The media used were: distilled water, 75% ethanol and 100% chlorophorm. Five repetitions were made for each group. The specimens were placed in a desiccator at 37°C for 24 h and, after that, at 23°C for 1 h to be weighed until a constant mass (m₁) was obtained. The discs were immersed separately into the 3 media for 7 days (G1) and 60 days (G2), and thereafter reweighed (m₂). The reconditioning in the desiccator was done until a constant mass (m₃) was obtained. Sorption and solubility were calculated and the data of G1 and the sorption data of G2 were subjected to two-way ANOVA and Tukey''s tests (p=0.05). The solubility data of G2 were analyzed by Kruskal-Wallis test (p=0.05). For G1 and G2, no statistically significant differences were found in sorption among curing techniques (p>0.05). The solubility values were negative, which means that there was mass gain. Regarding the storage media, in G2 chlorophorm had the highest sorption values. It may be concluded that the curing modes (C and PD I, II and III) did not affect the sorption of the tested composite resin. However, different storage media influenced sorption behavior. The solubility test demonstrated negative data, masking the real solubility.     

RELATIONSHIP BETWEEN THE DEGREE OF CONVERSION,SOLUBILITY AND SALIVARY SORPTION OF A HYBRID AND A NANOFILLED RESIN COMPOSITE: INFLUENCE OF THE LIGHT-ACTIVATION MODE

This study analyzed the relationship between the degree of conversion (DC), solubility, and salivary sorption of a hybrid (Filtek P 60) and a nanofilled resin composite (Filtek Supreme), and evaluated the influence of the light-activation mode on these properties. Two light-activation modes were used: Conventional (C; 850 mW/cm² for 20 s) and Soft-start (SS; 100-1,000 mW/cm² for 10 s + 1,000 mW/cm² for 10 s). The DC (%) was evaluated by FT-Raman spectroscopy. The solubility and salivary sorption were measured after immersion in artificial saliva for 7 days. Data were analyzed by ANOVA and Student-Newman-Keuls'' test and linear regression analysis (α = 0.05). The DC varied from 50.52% (nanofilled composite) to 57.15% (hybrid composite), and was influenced by the light-activation mode: C > SS. The solubility (0.45 μg/mm³) and salivary sorption (8.04 μg/mm³) of the nanofilled composite were greater than those of the hybrid composite (0.40 μg/mm³/ 6.87 μg/mm³), and were influenced by the light-activation mode: SS > C. Correlation was found between DC and solubility (r = - 0.89, p<0.05), as well as between solubility and salivary sorption (r = 0.95). These findings suggest that nanofilled composites may present higher degradation in the oral environment than hybrid ones. Soft-start light-activation mode may increase the solubility of resin composites.     

Hardness and diametral tensile strength of a hybrid composite resin polymerized with different modes and immersed in ethanol or distilled water media

OBJECTIVES: The aim of this in vitro study was to evaluate the microhardness and diametral tensile strength of a hybrid composite resin (Z250, 3M ESPE) polymerized with four different modes of light exposure and immersed in two different media. METHODS: Composite resin specimens were randomly polymerized according to the experimental groups (conventional, 550 mW/cm(2)/30 s; soft start, 300 mW/cm(2)/10 s + 550 mW/cm(2)/20 s; high intensity, 1060 mW/cm(2)/10 s; pulse delay, 550 mW/cm(2)/1 s + 60 s of waiting time + 550 mW/cm(2)/20 s) and immersed in one of two media (distilled water or absolute ethanol) for 24 h. After that, microhardness (M) and diametral tensile strength (DTS) tests were performed. RESULTS: For DTS, there were no statistical differences among the polymerization modes, however, ethanol medium groups presented statistically lower DTS (p < 0.05) than water medium. For the M test, samples immersed in ethanol medium presented lower M for almost all groups. Conventional mode presented higher M values for the groups immersed in water medium. In ethanol medium, conventional and pulse delay groups presented higher M values, statistically different (p < 0.05) from the high intensity group. For all experimental conditions, the top surface showed higher M than the bottom surface. SIGNIFICANCE: Different polymerization modes can be related to the different polymer structures formed, and consequently with different physical properties of resin composite. The immersion media can alter the physical properties of resin composites of different polymer structures.     

EVALUATION OF INTERNAL ADAPTATION OF CLASS V RESIN COMPOSITE RESTORATIONS USING THREE TECHNIQUES OF POLYMERIZATION

Objective:

The purpose of this in vitro study was to evaluate the internal adaptation of Class V composite restorations to the cavity walls using three different techniques of polymerization.

Methods:

Standard cavities were prepared on the buccal and lingual surfaces of 24 extracted human third molars with margins located above and below the cementoenamel junction. Restorations were placed in one increment using two restorative systems: 3M Filtek A110/ Single Bond (M) and 3M Filtek Z250/ Single Bond (H) in the same tooth, randomly in the buccal and lingual surfaces. Resin composites were polymerized using three techniques: Group 1 – Conventional (60 s - 600 mW/cm²); Group 2 – Soft-start (20 s – 200 mW/cm², 40 s - 600 mW/cm²); Group 3 – Pulse Activation (3 s - 200 mW/cm², 3-min hiatus, 57 s - 600 mW/cm²). Buccolingual sections were polished, impressions taken and replicated. Specimens were assessed under scanning electron microscopy up to X1000 magnification. Scores were given for presence or absence of gaps (0 – no gap; 1 – gap in one wall; 2 – gap in two walls; 3 – gap in three walls).

Results:

The mean scores of the groups were (±SD) were: G1M–3.0 (± 0.0); G2M–2.43 (± 0.8); G3M– 1.71 (± 0.9); G1H– 2.14 (± 1.2); G2H- 2.00 (± 0.8); G3H- 1.67 (± 1.1). Data were analyzed using Kruskal-Wallis and Dunnet’s tests. No statistically significant difference (p>0.05) was found among groups. Gaps were observed in all groups.

Conclusions:

The photocuring technique and the type of resin composite had no influence on the internal adaptation of the material to the cavity walls. A positive effect was observed when the slow polymerization techniques were used.     

Influence of light-exposure methods and depths of cavity on the microhardness of dual-cured core build-up resin composites

Objective

The purpose of this study was to evaluate the Knoop hardness number (KHN) of dual-cured core build-up resin composites (DCBRCs) at 6 depths of cavity after 3 post-irradiation times by 4 light-exposure methods.

Material and Methods

Five specimens each of DCBRCs (Clearfil DC Core Plus [DCP] and Unifil Core EM [UCE]) were filled in acrylic resin blocks with a semi-cylindrical cavity and light-cured using an LED light unit (power density: 1,000 mW/cm²)at the top surface by irradiation for 20 seconds (20 s), 40 seconds (40 s), bonding agent plus 20 seconds (B+20 s), or 40 seconds plus light irradiation of both sides of each acrylic resin block for 40 seconds each (120 s). KHN was measured at depths of 0.5, 2.0, 4.0, 6.0, 8.0, and 10.0 mm at 0.5 hours, 24 hours, and 7 days post-irradiation. Statistical analysis was performed using repeated measures ANOVA and Tukey''s compromise post-hoc test with a significance level of p<0.05.

Results

For both DCBRCs, at 0.5 hours post-irradiation, the 20 s and 40 s methods showed the highest KHN at depth of 0.5 mm. The 40 s method showed significantly higher KHN than the 20 s method at all depths of cavity and post-irradiation times, except UCE at depth of 0.5 mm (p<0.05). The 120 s method did not result in significantly different KHN at all depths of cavity and post-irradiation times (p>0.05). In DCP, and not UCE, at 24 hours and 7 days post-irradiation, the B+20 s method showed significantly higher KHN at all depths of cavity, except the depth of 0.5 mm (p<0.05).

Conclusion

KHN depends on the light-exposure method, use of bonding agent, depth of cavity, post-irradiation time, and material brand. Based on the microhardness behavior, DCBRCs are preferably prepared by the effective exposure method, when used for a greater depth of cavity.     

THE EFFECT OF DIFFERENT LIGHT-CURING UNITS ON TENSILE STRENGTH AND MICROHARDNESS OF A COMPOSITE RESIN

The aim of this study was to evaluate the influence of different light-curing units on the tensile bond strength and microhardness of a composite resin (Filtek Z250 – 3M/ESPE). Conventional halogen (Curing Light 2500 – 3M/ESPE; CL) and two blue light emitting diode curing units (Ultraled – Dabi/Atlante; UL; Ultrablue IS – DMC; UB3 and UB6) were selected for this study. Different light intensities (670, 130, 300, and 600 mW/cm², respectively) and different curing times (20s, 40s and 60s) were evaluated. Knoop microhardness test was performed in the area corresponding to the fractured region of the specimen. A total of 12 groups (n=10) were established and the specimens were prepared using a stainless steel mold composed by two similar parts that contained a cone-shaped hole with two diameters (8.0 mm and 5.0 mm) and thickness of 1.0 mm. Next, the specimens were loaded in tensile strength until fracture in a universal testing machine at a crosshead speed of 0.5 mm/min and a 50 kg load cell. For the microhardness test, the same matrix was used to fabricate the specimens (12 groups; n=5). Microhardness was determined on the surfaces that were not exposed to the light source, using a Shimadzu HMV-2 Microhardness Tester at a static load of 50 g for 30 seconds. Data were analyzed statistically by two-way ANOVA and Tukey''s test (p<0.05). Regarding the individual performance of the light-curing units, there was similarity in tensile strength with 20-s and 40-s exposure times and higher tensile strength when a 60-s light-activation time was used. Regarding microhardness, the halogen lamp had higher results when compared to the LED units. For all light-curing units, the variation of light-exposure time did not affect composite microhardness. However, lower irradiances needed longer light-activation times to produce similar effect as that obtained with high-irradiance light-curing sources.     

INFLUENCE OF LIGHT ENERGY DENSITY ON HEAT GENERATION DURING PHOTOACTIVATION OF DENTAL COMPOSITES WITH DIFFERENT DENTIN AND COMPOSITE THICKNESS

Objective:

The aim of this study was to determine the influence of different energy densities on the heat generated during photoactivation of Filtek Z250 (3M/ESPE) and Z100 (3M/ESPE) composite resins with different dentin and composite thickness.

Material and Methods:

The temperature increase was registered with a type-K thermocouple connected to a digital thermometer (Iopetherm 46). A chemically polymerized acrylic resin base was prepared to serve as a guide for the thermocouple and as a support for 0.5-, 1.0-, and 1.5-mm-thick bovine dentin discs. Circular elastomer molds (1.0 mm-height x 3.0-mm diameter or 2.0-mm height x 3.0-mm diameter) were adapted on the acrylic resin base to standardize the composite resin thickness. A conventional halogen light-curing unit (XL 2500, 3M/ESPE) was used with light intensity of 700 mW/cm². Energy density was calculated by the light intensity applied during a certain time with values of 28 J/cm² for Z100 and 14 J/cm² for Filtek Z250. The temperature change data were subjected to three-way ANOVA and Tukey''s test at 5% level.

Results:

The higher energy density (Z100) promoted greater temperature increase (p<0.05) than the lower energy density (Filtek Z250). For both composites and all composite thicknesses, the lowest dentin thickness (0.5 mm) yielded significantly higher (p<0.05) temperature increase than the other two dentin thicknesses. The 1-mm-thick composite resin layer yielded significantly higher (p<0.05) temperature changes for both composites and all dentin thicknesses.

Conclusions:

Temperature increase was influenced by higher energy density and dentin/composite thickness.     

Surface properties of multilayered,acrylic resin artificial teeth after immersion in staining beverages

Objective

To evaluate the effect of staining beverages (coffee, orange juice, and red wine) on the Vickers hardness and surface roughness of the base (BL) and enamel (EL) layers of improved artificial teeth (Vivodent and Trilux).

Material and Methods

Specimens (n=8) were stored in distilled water at 37°C for 24 h and then submitted to the tests. Afterwards, specimens were immersed in one of the staining solutions or distilled water (control) at 37°C, and the tests were also performed after 15 and 30 days of immersion. Data were analyzed using 3-way ANOVA and Tukey’s test (α=0.05).

Results

Vivodent teeth exhibited a continuous decrease (p<0.0005) in hardness of both layers for up to 30 days of immersion in all solutions. For Trilux teeth, similar results were found for the EL (p<0.004), and the BL showed a decrease in hardness after 15 days of immersion (p<0.01). At the end of 30 days, this reduction was not observed for coffee and water (p>0.15), but red wine and orange juice continuously reduced hardness values (p<0.0004). Red wine caused the most significant hardness changes, followed by orange juice, coffee, and water (p<0.006). No significant differences in roughness were observed for both layers of the teeth during the immersion period, despite the beverage (p>0.06).

Conclusions

Hardness of the two brands of acrylic teeth was reduced by all staining beverages, mainly for red wine. Roughness of both layers of the teeth was not affected by long-term immersion in the beverages.     

DEPTH OF CURE OF DENTAL COMPOSITES SUBMITTED TO DIFFERENT LIGHT-CURING MODES

Objective:

This study evaluated the depth of cure of five dental composites submitted to different light-curing modes.

Material and Methods:

Canal-shaped cavities with 5mm of length were prepared on the buccal surfaces of extracted third molars, and restored using P-60, A-110, Admira, Z-250 and Supreme resin composites. Materials were light-cured from the top, according to three modes (Group 1- Conventional (C): 500 mW/cm²/ 40 s; Group 2 – Soft-Start (SS):250 mW/cm²/ 20 s + 500 mW/cm²/ 20 s + 500 mW/cm²/ 10 s and Group 3 – LED: 250 mW/cm²/ 40 s). After that, cavity longitudinal surfaces were polished and marked with a millimeter scale of 4mm of length. Depth of cure was evaluated by means of Knoop hardness number (KHN), so that five indentations were performed at each millimeter. Original data were submitted to three-way ANOVA and Fisher''s LSD test (α = 0.01).

Results:

All materials presented a significant reduction on KHN from first to third millimeter. Regarding depth of cure, the results obtained for Conventional and Soft-Start modes were similar, but statistically superiors to those found for group 3 (LED). Conclusion: This performance may be related to the differences among energy densities obtained with different light-curing modes.     

INFLUENCE OF THE CURING METHOD ON THE POSTPOLYMERIZATION SHRINKAGE STRESS OF A COMPOSITE RESIN

The aim of this study was to evaluate the effect of different curing methods on the stress generated by the polymerization shrinkage of a restorative composite in two moments: immediately after light exposure and after 5 min. Photoactivation was performed using two different light sources: (1) xenon plasma arc (PAC) light (1,500 mW/cm² – 3s) and (2) a quartz-tungsten-halogen (QTH) light with three light-curing regimens: continuous exposure (40 s at 800 mW/cm² – CL); soft-start (10 s at 150 mW/cm² and 30 s at 800 mW/cm² - SS) and intermittent light [cycles of 4 s (2 s with light on at 600 mW/cm² and 2 s of light off), for 80s – IL]. The composite resin was applied between two 5-mm diameter metallic rods, mounted in a servohydraulic machine. The maximum stress was recorded immediately after light exposure (FF) and after 5 min (5F). The results were submitted to ANOVA and Tukey''s test (5%). For each method, the results obtained in FF and 5F were, respectively: CL (3.58 and 4.46 MPa); SS (2.99 and 4.36 MPa); IL (3.11 and 4.32 MPa) and PAC (0.72 and 3.27 MPa). The stress generated by the polymerization shrinkage during light exposure can be associated with the photoactivation method used. A significant increase in the stress level was observed during the post-curing period up to 5 min, for all evaluated methods.     

Temperature rise caused in the pulp chamber under simulated intrapulpal microcirculation with different light-curing modes

Objective:To evaluate and compare intrapulpal temperature rise with three different light-curing units by using a study model simulating pulpal blood microcirculation.Materials and Methods:The roots of 10 extracted intact maxillary central incisors were separated approximately 2 mm below the cement-enamel junction. The crowns of these teeth were fixed on an apparatus for the simulation of blood microcirculation in pulp. A J-type thermocouple wire was inserted into the pulp chamber through a drilled access on the palatal surfaces of the teeth. Four measurements were made using each tooth for four different modes: group 1, 1000 mW/cm² for 15 seconds; group 2, 1200 mW/cm² for 10 seconds; group 3, 1400 mW/cm² for 8 seconds; and group 4, 3200 mW/cm² for 3 seconds. The tip of the light source was positioned at 2 mm to the incisor''s labial surface.Results:The highest temperature rise was recorded in group 1 (2.6°C ± 0.54°C), followed by group 2 (2.57°C ± 0.62°C) and group 3 (2.35°C ± 0.61°C). The lowest temperature rise value was found in group 4 (1.74°C ± 0.52°C); this value represented significantly lower ΔT values when compared to group 1 and group 2 (P  =  .01 and P  =  .013, respectively).Conclusions:The lowest intrapulpal temperature rise was induced by 3200 mW/cm² for 3 seconds of irradiation. Despite the significant differences among the groups, the temperature increases recorded for all groups were below the critical value of 5.6°C.     

INFLUENCE OF DIFFERENT ADHESIVE SYSTEMS ON THE PULL-OUT BOND STRENGTH OF GLASS FIBER POSTS

This in vitro study evaluated the tensile bond strength of glass fiber posts (Reforpost – Angelus-Brazil) cemented to root dentin with a resin cement (RelyX ARC – 3M/ESPE) associated with two different adhesive systems (Adper Single Bond - 3M/ESPE and Adper Scotchbond Multi Purpose (MP) Plus – 3M/ESPE), using the pull-out test. Twenty single-rooted human teeth with standardized root canals were randomly assigned to 2 groups (n=10): G1- etching with 37% phosphoric acid gel (3M/ESPE) + Adper Single Bond + #1 post (Reforpost – Angelus) + four #1 accessory posts (Reforpin – Angelus) + resin cement; G2- etching with 37% phosphoric acid gel + Adper Scotchbond MP Plus + #1 post + four #1 accessory posts + resin cement. The specimens were stored in distilled water at 37°C for 7 days and submitted to the pull-out test in a universal testing machine (EMIC) at a crosshead speed of 0.5 mm/min. The mean values of bond strength (kgf) and standard deviation were: G1- 29.163 ± 7.123; G2- 37.752 ±13.054. Statistical analysis (Student''s t-test; α=0.05 showed no statistically significant difference (p<0.05) between the groups. Adhesive bonding failures between resin cement and root canal dentin surface were observed in both groups, with non-polymerized resin cement in the apical portion of the post space when Single Bond was used (G1). The type of adhesive system employed on the fiber post cementation did not influence the pull-out bond strength.     

The influence of "C-factor" and light activation technique on polymerization contraction forces of resin composite

Objectives

This study evaluated the influence of the cavity configuration factor ("C-Factor") and light activation technique on polymerization contraction forces of a Bis-GMA-based composite resin (Charisma, Heraeus Kulzer).

Material and Methods

Three different pairs of steel moving bases were connected to a universal testing machine (emic DL 500): groups A and B - 2x2 mm (CF=0.33), groups C and D - 3x2 mm (CF=0.66), groups e and F - 6x2 mm (CF=1.5). After adjustment of the height between the pair of bases so that the resin had a volume of 12 mm³ in all groups, the material was inserted and polymerized by two different methods: pulse delay (100 mW/cm² for 5 s, 40 s interval, 600 mW/cm² for 20 s) and continuous pulse (600 mW/cm² for 20 s). Each configuration was light cured with both techniques. Tensions generated during polymerization were recorded by 120 s. The values were expressed in curves (Force(N) x Time(s)) and averages compared by statistical analysis (ANOVA and Tukey''s test, p<0.05).

Results:

For the 2x2 and 3x2 bases, with a reduced C-Factor, significant differences were found between the light curing methods. For 6x2 base, with high C-Factor, the light curing method did not influence the contraction forces of the composite resin.

Conclusions

Pulse delay technique can determine less stress on tooth/restoration interface of adhesive restorations only when a reduced C-Factor is present.     

INFLUENCE OF A COBALT-CHROMIUM METAL FRAMEWORK ON SURFACE ROUGHNESS AND KNOOP HARDNESS OF VISIBLE LIGHT-POLYMERIZED ACRYLIC RESINS

Although visible light-polymerized acrylic resins have been used in removable partial dentures, it is not clear whether the presence of a metal framework could interfere with their polymerization, by possibly reflecting the light and affecting important properties, such as roughness and hardness, which would consequently increase biofilm accumulation. The aim of this study was to compare the roughness and Knoop hardness of a visible light-polymerized acrylic resin and to compare these values to those of water-bath- and microwave-polymerized resins, in the presence of a metal framework. Thirty-six specimens measuring 30.0 × 4.0 ± 0.5 mm of a microwave- (Onda Cryl), a visible light- (Triad) and a water-bath- polymerized (Clássico) (control) acrylic resins containing a cobalt-chromium metal bar were prepared. After processing, specimens were ground with 360 to 1000-grit abrasive papers in a polishing machine, followed by polishing with cloths and 1μm diamond particle suspension. Roughness was evaluated using a profilometer (Surfcorder SE 1700) and Knoop hardness (Kg/mm²) was assayed using a microhardness tester (Shimadzu HMV 2000) at distances of 50, 100, 200, 400 and 800 μm from the metal bar. Roughness and Knoop hardness means were submitted to two-way ANOVA and compared by Tukey and Kruskal Wallis tests at a 5% significance level Statistically significant differences were found (p<0.05) for roughness and Knoop hardness, with light-polymerized resin presenting the highest values (Ra = 0.11 μm and hardness between 20.2 and 21.4 Kg/mm²). Knoop values at different distances from the metal bar did not differ statistically (p>0.05). Within the limitations of this in vitro study, it was concluded that the presence of metal did not influence roughness and hardness values of any of the tested acrylic resins.     

INFLUENCE OF THE DISTANCE OF THE CURING LIGHT SOURCE AND COMPOSITE SHADE ON HARDNESS OF TWO COMPOSITES

This study evaluated the influence of curing tip distance, shade and filler particle size on Vickers microhardness (VHN) of composite resins. Two composites were tested: Filtek Z250 microhybrid (3M ESPE; shades A1 and A3.5) and Filtek Supreme nanofilled (3M ESPE; shades A1B and A3.5B). For each resin, 42 specimens (5 mm in diameter and 2 mm height) were prepared being 21 for each shade. The specimens were exposed using a 20-second exposure to a quartz-tungsten-halogen light source with an irradiance of approximately 560 mW/cm², at the following distances: 0 mm (surface contact), 6 mm and 12 mm from composite surface. Effectiveness of cure of different resins, shades and curing distances was determined by measuring the top and bottom hardness (VHN) of specimens using a digital microhardness tester (load: 50 g; dwell time: 45 seconds) 24 hours following curing. The hardness ratio was calculated by dividing VHN of the bottom surface by VHN of top surface. Three-way ANOVA and Tukey''s post-hoc test (p<0.05) revealed statistically significant differences for all analyzed factors. As for top hardness, as microhardness ratio (bottom/top), the factors shade, distance and composite filler particle size exerted influence on resin curing. Lighter shade composites (A1 and A1B) showed higher hardness values. At 6 and 12 mm curing tip distances, hardness was lower when compared to 0 mm. The microhybrid composite resin presented higheer hardness, being its microhardness ratio satisfactory only at 0 mm for both shades and at 6 mm for the lighter shade. The nanofilled composite resin did not present satisfactory microhardness at the bottom while the microhybrid composite resin had higher hardness than the nanofilled. Composite''s curing tip distance and shade can influence hardness.     

Surface hardness evaluation of different composite resin materials: influence of sports and energy drinks immersion after a short-term period

Objectives:

This study evaluated the effect of sports and energy drinks on the surface hardness of different composite resin restorative materials over a 1-month period.

Material and Methods:

A total of 168 specimens: Compoglass F, Filtek Z250, Filtek Supreme, and Premise were prepared using a customized cylindrical metal mould and they were divided into six groups (N=42; n=7 per group). For the control groups, the specimens were stored in distilled water for 24 hours at 37º C and the water was renewed daily. For the experimental groups, the specimens were immersed in 5 mL of one of the following test solutions: Powerade, Gatorade, X-IR, Burn, and Red Bull, for two minutes daily for up to a 1-month test period and all the solutions were refreshed daily. Surface hardness was measured using a Vickers hardness measuring instrument at baseline, after 1-week and 1-month. Data were statistically analyzed using Multivariate repeated measure ANOVA and Bonferroni''s multiple comparison tests (α=0.05).

Results:

Multivariate repeated measures ANOVA revealed that there were statistically significant differences in the hardness of the restorative materials in different immersion times (p<0.001) in different solutions (p<0.001). The effect of different solutions on the surface hardness values of the restorative materials was tested using Bonferroni''s multiple comparison tests, and it was observed that specimens stored in distilled water demonstrated statistically significant lower mean surface hardness reductions when compared to the specimens immersed in sports and energy drinks after a 1-month evaluation period (p<0.001). The compomer was the most affected by an acidic environment, whereas the composite resin materials were the least affected materials.

Conclusions:

The effect of sports and energy drinks on the surface hardness of a restorative material depends on the duration of exposure time, and the composition of the material.     

Composite resin color stability: influence of light sources and immersion media

Objective

This study evaluated the influence of light sources and immersion media on the color stability of a nanofilled composite resin.

Material and Methods

Conventional halogen, high-power-density halogen and high-power-density light-emitting diode (LED) units were used. There were 4 immersion media: coffee, tea, Coke^® and artificial saliva. A total of 180 specimens (10 mm x 2 mm) were prepared, immersed in artificial saliva for 24 h at 37±1ºC, and had their initial color measured with a spectrophotometer according to the CIELab system. Then, the specimens were immersed in the 4 media during 60 days. Data from the color change and luminosity were collected and subjected to statistical analysis by the Kruskall-Wallis test (p<0.05). For immersion time, the data were subjected to two-way ANOVA test and Fisher''s test (p<0.05).

Results

High-power-density LED (∆E=1.91) promoted similar color stability of the composite resin to that of the tested halogen curing units (Jet Lite 4000 plus - ∆E=2.05; XL 3000 - ∆E=2.28). Coffee (∆E=8.40; ∆L=-5.21) showed the highest influence on color stability of the studied composite resin.

Conclusion

There was no significant difference in color stability regardless of the light sources, and coffee was the immersion medium that promoted the highest color changes on the tested composite resin.     

EFFECT OF DIFFERENT POLISHING SYSTEMS ON THE SURFACE ROUGHNESS OF MICROHYBRID COMPOSITES

The use of composite resins in dentistry is well accepted for restoring anterior and posterior teeth. Many polishing protocols have been evaluated for their effect on the surface roughness of restorative materials. This study compared the effect of different polishing systems on the surface roughness of microhybrid composites. Thirty-six specimens were prepared for each composite [Charisma^® (Heraeus Kulzer), Fill Magic^® (Vigodent), TPH Spectrum^® (Dentsply), Z100^® (3M/ESPE) and Z250^® (3M/ESPE)] and submitted to surface treatment with Enhance^® and PoGo^® (Dentsply) points, sequential Sof-Lex XT^® aluminum oxide disks (3M/ESPE), and felt disks (TDV) combined with Excel^® diamond polishing paste (TDV). Average surface roughness (Ra) was measured with a mechanical roughness tester. The data were analyzed by two-way ANOVA with repetition of the factorial design and the Tukey-Kramer test (p<0.01). The F-test result for treatments and resins was high (p<0.0001 for both), indicating that the effect of the treatment applied to the specimen surface and the effect of the type of resin on surface roughness was highly significant. Regarding the interaction between polishing system and type of resin used, a p value of 0.0002 was obtained, indicating a statistically significant difference. A Ra of 1.3663 was obtained for the Sof-Lex/TPH Spectrum interaction. In contrast, the Ra for the felt disk+paste/Z250 interactions was 0.1846. In conclusion, Sof-Lex polishing system produced a higher surface roughness on TPH Spectrum resin when compared to the other interactions.     

EFFECT OF DIFFERENT PROPHYLAXIS METHODS ON SOUND AND DEMINERALIZED ENAMEL

Considering the importance of professional plaque control for caries prevention, this study comprised an in vitro evaluation of wear by two prophylaxis methods (sodium bicarbonate jet – Profident and pumice and brush) on sound bovine enamel and with artificial carious lesions. Sixty enamel fragments were employed (4x4mm), which were divided into 4 groups: GI – 15 sound blocks treated with pumice and brush; GII – 15 sound blocks treated with Profident; GIII – 15 demineralized blocks treated with pumice and brush, and GIV – 15 demineralized blocks treated with Profident. In the fragments of Groups III and IV, artificial carious lesions were simulated by immersion in 0.05M acetic acid solution 50% saturated with bovine enamel powder at 37^oC for 16h. The specimens were submitted to the prophylactic treatments for 10 seconds. Wear analysis was performed by profilometer and revealed the following results: 0.91μm – GI; 0.42μm – GII; 1.6μm – GIII, and 0.94μm – GIV. The two-way ANOVA and Tukey''s test (p<0.05) revealed significant difference between all groups. Scanning electron microscopy images were employed to illustrate the wear pattern, with observation of larger alteration on the demineralized enamel surface (GIII; GIV), round-shaped wear on GI and GIII and blasted aspect on GII and GIV. The study indicated that the demineralized enamel presented more wear than the sound enamel, and the brush led to larger wear when compared to Profident.